Variable Gain Amplifier for CMOS Image Sensor Signal Readout
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Solution Overview
Problem
CMOS type solid-state image pickup devices face challenges in achieving high-definition static and moving image pickup, particularly with increased pixel counts, where readout through memory becomes crucial for moving images, and existing methods like pixel addition affect noise levels and signal-to-noise ratio (S/N) differently across technologies like CCD and CMOS.
Innovation Solution
A solid-state image pickup device with variable gain amplifying means connected to each output line, allowing for two modes of readout: direct reading for still images and signal addition for moving images, optimizing S/N and dynamic range by adjusting gain levels based on lighting conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If pixel addition is performed to reduce readout burden for moving images, then the readout speed requirement is reduced, but the signal-to-noise ratio deteriorates due to averaging multiple pixel signals
Solution Approach 1:
The invention changes the gain parameter of the variable gain amplifier based on the readout mode. In pixel addition mode, the gain is set to a higher level to amplify the averaged signal and compensate for noise. In direct readout mode, the gain is set to a lower level to maintain dynamic range. This parameter change allows the system to optimize both readout speed and signal-to-noise ratio for different operating conditions.
2Measurement precision
If high gain is used to improve signal-to-noise ratio in pixel addition mode, then noise is reduced, but dynamic range is reduced
Solution Approach 1:
The invention employs a variable gain amplifier that can dynamically adjust its gain level based on the operating mode. The gain is set to a first level (higher) when pixel addition is performed to improve signal-to-noise ratio, and set to a second level (lower) when direct readout is performed to maintain dynamic range. This dynamic adjustment allows the system to optimize performance for each specific mode without permanent compromise.
3Measurement precision
If analog memory is provided for each readout line to enable pixel addition, then moving image quality is improved, but chip area increases
Solution Approach 1:
The invention makes the analog memory cells serve multiple functions: they are used for pixel addition in moving image mode, and also for signal storage and processing in still image mode. By making the memory structure multi-functional, the patent avoids the need for separate memory structures for different modes, thereby reducing overall chip area while maintaining high image quality for moving images.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables high-quality image pickup with improved S/N and wide dynamic range in varying illuminance conditions, minimizing chip area by using necessary analog memory and column amplifiers, suitable for both static and moving image applications.
Implementation Method 1
a plurality of pixels perform photoelectric conversion on incident light
Data Source
AI summary
A solid-state image pickup device includes an adder adding signals from pixels to achieve a high S/N, while performing both static image and moving image pickup. The device has a pixel unit having pixels arranged two-dimensionally and outputs pixel signals derived by photoelectric conversion. The device operates in a first mode of reading a pixel signal of every pixel, and a second mode of adding and reading a plurality of pixel signals. Variable gain column amplifiers perform readout at different gains in the first and second modes. The device also has output lines where output signals from the pixels arranged in one line are outputted respectively, and at least one of the variable gain amplifier is connected to each of the output lines. The gain at the time of readout in the second mode is higher than the gain at the time of readout in the first mode.